Why is Mexican Blown Glassware also called Bubble Glass ?

Mexico is very well known for hand blown drinking glasses, the most popular of them characterized by a blue band blown into the rim. All glasses are 100% Lead Free.
If you hold a glass up to the sunlight and look through it, you will see hundreds of trapped bubbles through out the glass, this is normal and part of the hand blown process.
This is why originally it was called "bubble glass". Now days glass blowers that can blow large bubbles inside the glassware are considered to be "Master Blowers".